Since the advent of printers, and specifically for low cost printers for personal computers, a variety of inkjet printing mechanisms have been developed and utilized in the industry. These inkjet printing mechanisms include the piezoelectric type, the electrostatic type and the thermal bubble type, etc. After the first thermal inkjet printer becomes commercially available in the early 1980's, there has been a great progress in the development of inkjet printing technology.
In an inkjet printer, a liquid droplet injector is one of the key mechanisms. To provide a high-quality and reliable inkjet printer, the availability of a liquid droplet injector capable of supplying high-quality droplets at high-frequency and high-spacial resolution is critical.
Presently, there are two types of inkjet printers that are available in the marketplace, the piezoelectric type and the thermal type. The thermal inkjet system, also known as thermal bubble inkjet system, as thermally driven bubble system or as bubble jet system utilizes bubble to eject ink droplets out of an ink supply chamber, while piezoelectric printers utilize piezoelectric actuators to pump ink out from a reservoir chamber. The principle of operation for a thermal bubble inkjet system is that an electrical current is first conducted to the heater by an electrode to boil liquid in an ink reservoir chamber. When the liquid is in a boiling state, bubble forms in the liquid and expands and thus functions as a pump to eject a fixed quantity of liquid from the reservoir chamber through an orifice and then forms into droplets. When the electrical current is turned-off, the bubble generated collapses and liquid refills the chamber by capillary force.
When evaluating the performance of a thermal bubble inkjet system, factors such as droplet ejection frequency, cross-talk between adjacent chambers and the generation of satellite droplets are considered. Two of these performance factors, i.e. the satellite droplets, which degrade the sharpness of the image produced and the cross-talk between adjacent chambers and flow channels which decreases the quality and reliability of the inkjet system are frequently encountered. In order to improve the performance of a thermal bubble inkjet system, these drawbacks must be corrected overcome.
In a copending application, Attorney Docket No. 64600-090, assigned to the common assignee of the present application which is hereby incorporated in its entirety, a thermal bubble type inkjet head that is equipped with a rapid ink refill mechanism and an off-shooter heater and a method for fabricating the head are disclosed. While the thermal bubble type inkjet head provides greatly improved results over the conventional thermal type inkjet head, the fabrication process for the head has been problematic due to overheating occurring in during the sputtering process of the metal seed layer or over-exposure of a second thick photoresist on top of the first thick photoresist layer. The overheating or over-exposure of the first thick photoresist layer affects the developing process of the layer.
It is therefore an object of the present invention to provide a micro-droplet generator, particularly related to micro-fluidic head that does not have the drawbacks or the shortcomings of the conventional thermal bubble injection head.
It is another object of the present invention to provide a micro-fluidic injection head that is equipped with a light-absorbing layer in between two photoresist layers for preventing overheating and over-exposure of the photoresist layers.
It is a further object of the present invention to provide a method for fabricating a micro-fluidic injection head that utilizes a symmetrical off-shooter heater to generate liquid droplets.
It is another further object of the present invention to provide a micro-fluidic injection head that is equipped with a liquid reservoir chamber.
It is yet another object of the present invention to provide a method for fabricating a micro-fluidic injection head that is equipped with a symmetrical heater.
It is still another further object of the present invention to provide a method for fabricating a micro-fluidic injection head that is equipped with a symmetrical heater utilizing two separate thick photoresist deposition processes and a nickel-containing material electroplating process.